D.I. Wilson

Enhanced cleaning of whey protein soils using pulsed flows.

Abstract Enhancement of alkali-based cleaning-in-place (CIP) of whey protein deposits by flow pulsing was investigated using low frequency (⩽2 Hz) fluid pulses with amplitudes an order of magnitude greater than the steady flow velocity. Flow pulses were generated using (i) a bellows unit and (ii) a piston device. The effect of pulsing was studied at a steady flow Reynolds number of 580, where pulsing at 2 Hz was found to increase heat transfer by up to 100%. Whey protein deposits were generated in a tubular heat exchanger and cleaned using 0.5 wt% NaOH at 50°C. Enhancement of cleaning rates varied up to 250% and depended on the initial amount of deposit present, the pulsing frequency and pulse amplitude. The increase in cleaning rate was most sensitive to the difference in pulse and steady flow velocities and the presence of reverse flow. Simultaneous protein removal and heat transfer resistance measurements showed that flow pulsing strongly affected the cleaning behaviour after the initial deposit swelling stage, breaking down the swollen deposit matrix by some fatigue mechanism.

Mitigation of Crude Oil Refinery Heat Exchanger Fouling Through Retrofits Based on Thermo-Hydraulic Fouling Models

Crude oil fouling in refinery preheat exchangers is a chronic operating problem that compromises energy recovery in these systems. Progress is hindered by the lack of quantitative knowledge of the dynamic effects of fouling on exchanger heat transfer and pressure drop. The concept of a thermal ‘fouling threshold’, first introduced by Ebert and Panchal, is revisited here alongside models of hydraulic effects of fouling to provide a graphical tool, the modified temperature field plot, for assessing chronic chemical reaction fouling effects in refinery heat exchangers. Fouling data of varying quality, collected from pilot plant and refinery operation, were compared with two previously published threshold fouling models and one based on the Epstein deposition model. The model by Epstein showed the best agreement, primarily because it can accommodate fouling that is mass transfer as well as reaction controlled. The hydraulic analysis indicated that the simple slab approximation for fouling layers gave a reasonably good mapping between heat transfer and pressure drop effects as long as roughness contributions are not significant. Where roughness effects (or tube blockage) are important, the relationship between thermal and hydraulic performance is not straightforward. A case study, based on the network described by Panchal and Huang-Fu, is used to illustrate the thermo-hydraulic effects of fouling and the application of the modified temperature field plot.

Chemical reaction fouling: A review

Abstract Recent research on fouling of organic fluids is renewed. Fouling in organic mixtures can be caused by numerous reactions, including autoxidation, polymerization and thermal decomposition. Understanding of autoxidation processes and their link to fouling has developed markedly in the past few years. By contrast, for fouling under non-oxidative conditions, the chemical and physical processes have not been adequately explored.

Cleaning-in-Place of Whey Protein Fouling Deposits: Mechanisms Controlling Cleaning

The processes involved in alkali-based cleaning-in-place of whey protein deposits were investigated using cleaning solutions of 0.5 wt% NaOH over a range of surface temperatures (20–80°C) and flow rates ( Re = 500–5000). Cleaning was quantified by measuring both mass removal and the change in the thermal resistance of the deposits. The results confirmed that cleaning involved three stages, namely deposit swelling, uniform erosion and a final decay phase. The evolution of structure in the protein network on contacting NaOH was elucidated with SEM and surface fixation techniques on samples generated by a short contact time apparatus. The effects of temperature and flow rate on the cleaning rate changed between the uniform and breakdown stage. The protein removal rate in the uniform stage was strongly dependent on conditionsat the deposit/solution interface, while that in the decay phase was more sensitive to flow rate (i.e. surface shear stress). Reaction and diffusion of protein within the swollen deposit matrix appear to control the uniform cleaning rate. Simultaneous measurements of thermal resistance and protein removal did not show a simple correlation and suggest that existing models for cleaning require further development.

Challenges in Cleaning: Recent Developments and Future Prospects

Abstract There is considerable scope for the optimization of processes subject to fouling by effective management of cleaning. The cleaning cycle starts with the (often complex) material generated during the fouling cycle. The nature of the deposit determines the most appropriate cleaning method, which can often be optimized significantly via the knowledge of the key mechanisms involved in deposit removal. Links between deposit aging and cleanability need to be established and quantified. There is a wide range of cleaning methods available, and attention is focused here on cleaning-in-place (CIP) techniques. Modern instrumentation allows cleaning (and deposit materials behavior) to be probed to greater degree than ever before, but the removal technology is only part of the cleaning process. Monitoring and validation of cleaning are equally important, particularly for the process plant used in flexible manufacture or subject to batch assurance requirements. Individual sensors are unlikely to meet all monitoring criteria, so future approaches will require the reconciliation and interpretation of online data from multiple devices. Many industries stand to learn from the practice and approaches in the food, pharmaceuticals, and electronics sectors, where these concepts are well established. The definition of cleanliness will vary from sector to sector, but the needs of minimizing environmental impact, accurate monitoring, assurance, and suitable training for operators are common to all.

Effects of liquid phase migration on extrusion of microcrystalline cellulose pastes.

The behaviour of water-based microcrystalline cellulose pastes undergoing ram extrusion has been investigated. Factors affecting the redistribution of water within the extruding paste and the upstream barrel compact, such as the initial water content, extrusion rate and die geometry, have been considered. The rates of dewatering for these given systems were characterised by the gradients of the extrusion pressure-ram displacement profiles. A linear relationship between the pressure-displacement gradient and the inverse square root of the paste velocity was obtained for a given paste and extrusion geometry. At velocities where water migration was significant, the extrudate was found to have a higher water content than that of the paste in the barrel at any given time; both the extrudate and the barrel paste decreased in water content with increasing ram displacement. Spheronisation of extrudate samples has shown that the redistribution of liquid during extrusion is an important factor affecting the quality of the spheres. A paste flow model, incorporating pseudo-plastic and shear deformation terms, was used to predict the change in extrusion pressures caused by liquid phase migration. The model parameters were obtained as functions of water content and gave good agreement with the experimental extrusion profiles.

Investigation of Whey Protein Deposit Properties Using Heat Flux Sensors

Heat exchanger fouling due to whey proteins was investigated in a concentric-tube device using aqueous solutions of 3.5 wt% whey protein concentrate.The void (liquid) fraction of the deposit changed as the fouling mechanism changed from surface reaction control to mixed bulk reaction and mass transfer control. The thermal resistance of deposits and their effective thermal conductivity was measured in situ using a novel technique based on a heat flux sensor. This method gave values of (effective deposit thermal conductivity×density, ρ f λ f) around 470Wkgm−4K−1 for deposits exposed to wall temperatures less than 85° C. Deposits formed at higher wall temperatures showed the effects of ageing and gave a larger value of ρ f λ f.

Fouling in Crude Oil Preheat Trains: A Systematic Solution to an Old Problem

A major cause of refinery energy inefficiency is fouling in preheat trains. This has been a most challenging problem for decades, due to limited fundamental understanding of its causes, deposition mechanisms, deposit composition, and impacts on design/operations. Current heat exchanger design methodologies mostly just allow for fouling, rather than fundamentally preventing it. To address this problem in a systematic way, a large-scale interdisciplinary research project, CROF (crude oil fouling), brought together leading experts from the University of Bath, University of Cambridge, and Imperial College London and, through IHS ESDU, industry. The research, coordinated in eight subprojects blending theory, experiments, and modeling work, tackles fouling issues across all scales, from molecular to the process unit to the overall heat exchanger network, in an integrated way. To make the outcomes of the project relevant and transferable to industry, the research team is working closely with experts from many world leading oil companies. The systematic approach of the CROF project is presented. Individual subprojects are outlined, together with how they work together. Initial results are presented, indicating that a quantum progress can be achieved from such a fundamental, integrated approach. Some preliminary indications with respect to impact on industrial practice are discussed.

Optimization of Scheduling of Cleaning in Heat Exchanger Networks Subject to Fouling: Sugar Industry Case Study

Fouling of heat exchangers in the food industry results in frequent cleaning and an operational problem in scheduling production and cleaning periods. The complexity of the problem increases when a network involving more than one exchanger is involved, and requires a solution using integer programming techniques. A new modelling formulation has been developed to solve the resulting MINLP problem and provides near-optimal results. Application of the technique is illustrated with a case study of the raw juice preheat train in a sugar refinery featuring a network of 11 exchangers. Data reconciliation of plant information was used to generate linear fouling models for the simulation and the solver results are compared with current operating practice.

Investigation of alkaline cleaning-in-place of whey protein deposits using dynamic gauging

A novel thickness measurement technique (DYNA-PROBE) allows the study of the behaviour of layers of soft material undergoing cleaning in flowing liquids, in situ and in real time without contacting the surface. The technique is demonstrated here in a study of the swelling and removal of whey protein films related to cleaning-in-place of dairy heat exchanger fouling deposits. The experimental protocol also allows the gauge to be calibrated in situ after each test, yielding measurement accuracies of ±10μm. Cleaning experiments also featured simultaneous measurement of the mass of protein removed and the thermal resistance of the foulant layer, via a commercial heat flux sensor. Experiments performed over a range of solution concentrations (0.3–2.0 wt% NaOH), temperatures (20–50°C) and velocities (0.03–0.30 ms −1 ; Re = 500–10,000) indicated the existence of an optimal cleaning solution concentration and several other features reported by previous workers. New information provided by the technique, including the sensitivity to shear of the swollen deposit, yields new evidence permitting integration of several conflicting earlier hypotheses on protein cleaning behaviour.